Students with disorders of intellectual development (ID) experience challenges in reading and writing, indicating the need for research-based interventions. This systematic review and meta-analysis investigated the effects of reading and writing interventions for students aged 4–19 with disorders of ID using randomized controlled trials (RCTs) and quasi-experimental designs (QEDs). We conducted electronic searches of relevant databases, backward and forward searches, and contacted experts in the field. Based on predefined criteria, nine studies were included in the systematic review, and seven were included in the meta-analysis. The reading interventions included decoding strategies, often combined with sight-word and supplemental instructions appropriate to the participants’ adaptive and cognitive skills. None of the studies aimed to increase writing skills. The overall mean effect size from the reading interventions for trained reading was large (g = 0.95, 95% CI = [0.51, 1.38]), for transfer reading small-to-moderate (g = 0.49, 95% CI = [0.20, 0.78]) and for transfer writing small (g = 0.04, 95% CI = [−0.36, 0.44]). Students with disorders of ID can benefit from reading interventions combining decoding strategies and sight word reading. There is a need for RCT and QED studies investigating writing interventions for students with disorders of ID only.

Students with disorders of intellectual development (ID) often experience writing difficulties, and effective interventions are highly needed. This systematic review and meta-analysis of single-case experimental design (SCED) studies summarize the effects of writing interventions for students with disorders of ID aged 4–19 years. We conducted a systematic search of seven databases, ancestral and forward searches of relevant sources, and contacted well-known authors in the field. Fifteen and 10 studies were included in the systematic review and meta-analyses, respectively. The overall results indicate that the participants improved their writing skills, with a large between-case standardized mean difference (BC-SMD) effect on the number of words and sentences written (BC-SMD = 1.22) and on the quality of paragraph and story writing (BC-SMD = 1.39). Students with disorders of ID can benefit from writing interventions, and the study results may provide practitioners with important insight into promising writing instructions and materials. There is a need for high-quality research targeting encoding (i.e., transforming sound into letters) skills for early school-age students with disorders of ID.